This invention relates to the cooling of gear drives, and particularly to apparatus for converting the kinetic energy of splashing lubricant into mechanical energy which is employed to cool the gear drive.
It is common to use a system of splash lubrication to lubricate the meshing gearing and bearings of enclosed gear drive units such as speed reducers. The splash lubrication system involves partially immersing one of the rotating elements, usually a large gear, into an oil bath which is contained within the housing which also acts as a reservoir. As the element revolves, it dips into the oil or other lubricant and carries it along to the meshing gearing. Oil is also thrown off of the rotating gearing due to centrifugal force and its typically caught and collected in various troughs which lead through passages to the bearings so that the collected oil can lubricate the bearings.
The lubricant in such a system is heated by the gearing passing through it and also by the frictional losses due to the gear mesh and bearings. The oil must also function to conduct heat away from the meshing gearing and bearings. The amount of oil required will depend upon the amount of heat generated and the area of the housing which the oil can contact and through which the heat can be dissipated to the environment. As the velocity of the rotating gear at the pitch line increases, the heat losses due to the gear passing through the oil are increased by an exponential function. As a result, it has been typical to place an oil pan around the gear to minimize the amount of oil that the gear will contact as it revolves. The amount of oil entering the pan is controlled to provide sufficient lubrication for the revolving elements. This is typically done by providing a series of holes or slots in the pan at its low point. As the gear revolves, it will act as a pump and pull oil from the surrounding oil bath through the hole or slot into the pan. Oil is also forced through the holes or slots by the hydrostatic head of oil above the holes. The revolving gear picks up the entering oil and imparts its velocity to the oil thereby giving the oil kinetic energy. As the oil leaves the oil pan, it is thrown off the gear and out of the pan at a significant velocity which is close to the velocity of the pitch line of the gear. The kinetic energy of the oil is released in the form of shear energy as the oil strikes the interior surfaces of the housing. Heat is transferred to the housing by conduction, convection or radiation.
The amount of heat generated by a speed reducer or other enclosed gear drive can be considerable. Severe damage may occur if the speed reducer creates heat faster than it can be dissipated. To assist in dissipating the heat transferred to the housing, cooling fans have been typically employed on the input shafts to create a flow or air over the exterior surface of the housing.